Magnetoresistive (MR) array technology is utilized in a variety of commercial, consumer and industrial detection applications. In some conventional MR systems an apparatus can be provided for determining the position of a member movable along a path. In such a device, a magnet can be attached to the movable member and an array of magnetic field transducers are located adjacent the path. As the magnet approaches, passes and moves away from a transducer, the transducer provides a varying output signal, which can be represented by a single characteristic curve that is representative of any of the transducers.
To determine the position of the movable member, the transducers are electronically scanned and data is selected from a group of transducers having an output that indicates relative proximity to the magnet. A curve-fitting algorithm can then be utilized to determine a best fit of the data to the characteristic curve. By placement of the characteristic curve along a position axis, the position of the magnet and therefore the movable member may be determined.
In another conventional MR device, a position determining apparatus can be implemented, which includes a magnet that is attached to a movable member that moves along a predefined path of finite length. An array of magnetic field transducers can be located adjacent to the predefined path. The transducers can provide an output signal as the magnet approaches passes and moves away from each transducer. A correction mechanism can also be provided to correct for residual error caused by the non-linearity of the transducers.
Such a correction mechanism preferably approximates the residual error with a predetermined function, and applies correction factors that correspond to the predetermined function to offset the residual error. By correcting for the non-linearity of the transducers, the length of the magnet may be reduced and/or the spacing of the transducers may be reduced.
An example of a conventional magnetic sensing approach is disclosed, for example, in U.S. Pat. No. 5,589,769, “Position Detection Apparatus Including a Circuit for Receiving a Plurality of Output Signal Values and Fitting the Output Signal Values to a Curve,” which issued to Donald R. Krahn on Dec. 31, 1996, and is assigned to Honeywell International Inc. Another example of a magnetic sensing approach is disclosed in U.S. Pat. No. 6,097,183, “Position Detection Apparatus with Correction for Non-Linear Sensor Regions,” which issued to Goetz et al. on Aug. 1, 2000 and is also assigned to Honeywell International Inc. U.S. Pat. Nos. 5,589,769 and 6,097,183 are incorporated herein by reference in their entirety. Such MR-based devices generally utilize discrete components on a Printed Circuit Board (PCB) assembly to yield the resulting function.
One of the problems with magnetoresistive sensors, particularly anisotropic magnetoresistive (AMR) sensors based on an array configuration, is that thermal expansion physically alters the relative position of the magnetoresistive sensors not only with respect to themselves but with respect to the magnet being sensed. This, in turn, induces an error in the magnetoresistive array positing determining algorithm being utilized. Thus, it is believed that a solution to this problem involves developing new methodologies and systems for compensating for thermal expansion. Such new solutions are disclosed in further detail herein.